[CF-metadata] New CoordinateType: Spectral?

From: Jonathan Gregory <j.m.gregory>
Date: Sun, 7 Apr 2013 22:24:08 +0100

Dear Aleksandar

> I know this will likely end up as a trac ticket but would like first
> to gauge the community's opinion about defining a new coordinate type.
> Satellite data originates as measurements at a number of intervals of
> the electromagnetic spectrum. These intervals are commonly referred to
> as bands or channels. Deciding on how to store the band information is
> one of the key issues toward a standardized representation for
> satellite data.
>
> The convention seems to allow storing of band information either as a
> numerical coordinate variable or as a string auxiliary coordinate
> variable.

Yes, the CF standard could handle both of those, without any modification.
A trac ticket may not be needed. I certainly think there is no problem at
all for a numerical coordinate of band wavelength. You need only to propose
a new standard name for it, if one is needed. There is already a generic
standard name of radiation_wavelength, included for use as a coord variable
just as in your first example. If you need something more specific, I would
suggest sensor_radiation_wavelength. The coord values for this would be the
central wavelengths, and you could also supply bounds specifying the range
of wavelengths covered by the sensor.

Although string-valued auxiliary coordinate variables are possible already,
as used in your second example, I would argue they are less useful as
metadata than numerical ranges. That is because the main use of CF is to
support intercomparison of datasets, which is better-defined if numbers are
used. If there are widely used definitions of named wavelength bands,
required for intercomparison of many datasets, a standard_name could be
defined with a number of permitted string values. I think this extension
could probably be seen as a new standard_name, not requiring a change to
the conventions, although it could be explicitly mentioned in section 6 like
Roy is proposing for biological taxa.

Best wishes

Jonathan
Received on Sun Apr 07 2013 - 15:24:08 BST